In semiconductor fabrication processes, when features in a single layer of a semiconductor device are positioned closer than patterning resolution permits, multiple masks are often used in order to pattern the features. The features of the single layer of the semiconductor device are separated into different masks so that each mask includes features which are separated by a distance equal to or greater than a patterning resolution parameter. The process is called n-patterning based on the number of masks used to form the layer. For example, in some instances, a process using two masks is called double patterning; while a process using four masks is called quadruple patterning.
While designing a semiconductor device, designers will lay out the features of the semiconductor device in a layout pattern. These layout patterns include commonly used structures which are stored as standard cells in a cell library. A cell library is a database of standard cells which a designer can use in order to efficiently insert commonly used structures in a layout pattern while avoiding the extra task of designing each structure for each different semiconductor device. In some instances, the cell libraries include rules for placement of elements in order to assist with a coloring process.